The most common glass composition for making continuous glass fiber strands is “E-Glass.” The liquidus temperature of E-Glass is approximately 2100° F. (1149° C.) or lower. One advantage of E-Glass is that its liquidus temperature allows operating temperatures for producing glass fibers to be approximately 1900° F. to 2400° F. (1038° C. to 1316° C.). The ASTM classification for E-glass fiber yarns used in printed circuit boards and aerospace applications defines the composition to be 52 to 56 weight % SiO2, 16 to 25 weight % CaO, 12 to 16 weight % Al2O3, 5 to 10 weight % B2O3, 0 to 5 weight % MgO, 0 to 2 weight % Na2O and K2O, 0 to 0.8 weight % TiO2, 0.05 to 0.4 weight % Fe2O3 and 0 to 1.0 weight % Fluorine.
Boron-free fibers are sold under the trademark ADVANTEX (Owens Corning, Toledo, Ohio, USA). Boron-Free fibers, such as are disclosed in U.S. Pat. No. 5,789,329, incorporated herein by reference in its entirety, offer a significant improvement in operating temperatures over boron-containing E-glass. Boron-Free glass fibers fall under the ASTM definition for E-glass fibers for use in general-use applications.
S-Glass is a family of glasses composed primarily of the oxides of magnesium, aluminum, and silicon with a chemical composition that produces glass fibers having a higher mechanical strength than E-Glass fibers. The composition for forming S-Glass includes approximately 65 weight % SiO2, 25 weight % Al2O3, and 10 weight % MgO. S-glass has a composition that was originally designed to be used in high-strength applications such as ballistic armor.
R-Glass is a family of glasses that are composed primarily of the oxides of silicon, aluminum, magnesium, and calcium with a chemical composition that produces glass fibers with a higher mechanical strength than E-Glass fibers. R-Glass has a composition that contains approximately 58-60 weight % SiO2, 23.5-25.5 weight % Al2O3, 14-17 weight % CaO plus MgO, 0% B2O3, 0% F2 and less than 2 weight % miscellaneous components. R-Glass contains more alumina and silica than E-Glass and requires higher melting and processing temperatures during fiber forming. Typically, the melting and processing temperatures for R-Glass are at least 160° C. higher than those for E-Glass. This increase in processing temperature requires the use of a high-cost platinum-lined melter. In addition, the close proximity of the liquidus temperature to the forming temperature in R-Glass requires that the glass be fiberized at a viscosity lower than E-Glass, which is customarily fiberized at or near 1000 poise. Fiberizing R-Glass at the customary 1000 poise viscosity would likely result in glass devitrification, which causes process interruptions and reduced productivity.
Tables IA-IE set forth the compositions for a number of conventional high-strength glass compositions.
TABLE I-ARUSSIAN CONTINUOUSChineseROVING NITTOBONITTOBOHighMAGNESIUM “T”“T”StrengthALUMINO-Glass FabricGlass FabricConstituentglassSILICATE“B”(Yarn) “C”SiO255.0855.8164.5864.64CaO0.330.380.440.40Al2O325.2223.7824.4424.57B2O31.850.030.03MgO15.9615.089.959.92Na2O0.120.0630.080.09Fluorine0.030.0340.037TiO20.0232.330.0190.018Fe2O31.10.3880.1870.180K2O0.0390.560.0070.010ZrO20.0070.15Cr2O30.0110.0030.003Li2O1.63CeO2
TABLE I-BNittoNittoNitto Vetrotex SaintPolotskBosekiBosekiBoseki TEGobain SR GlassSTEKLOVOLOKNOA&PNT6030Glass RST-Stratifils SR CGHigh Strength ConstituentYarnYarn220PA-535CS250 P109GlassSiO265.51  64.60 64.20 63.90 58.64 CaO 0.44   0.58  0.63  0.26  0.61 Al2O324.06  24.60 25.10 24.40 25.41 B2O3 0.04 MgO 9.73   9.90  9.90 10.00 14.18 Na2O 0.04   0.06  0.020 0.039 0.05 Fluorine 0.07   0.02 TiO2 0.016  0.000 0.000 0.210 0.624Fe2O3 0.067  0.079 0.083 0.520 0.253K2O 0.020  0.020 0.020 0.540 0.35 ZrO2 0.079 Cr2O3 0.0010 0.001 0.023Li2OCeO2
TABLE I-CChinese HighChinese HighZentronAdvancedStrength StrengthS-2SOLAISGlassYarnGlassGlassGlassYarnsConstituent(8 micron)RovingRovingSampleR GlassSiO255.22  55.49 64.74 64.81 58.46 CaO 0.73   0.29  0.14  0.55  9.39 Al2O324.42  24.88 24.70 24.51 24.55 B2O3 3.46   3.52  0.02  0.04 MgO12.46  12.28 10.24  9.35  5.91 Na2O 0.104  0.06  0.17  0.16  0.079Fluorine 0.07   0.02  0.054TiO2 0.32   0.36 0.015 0.04  0.196Fe2O3 0.980  0.9300.045 0.238 0.400K2O 0.240  0.1500.005 0.03  0.67 ZrO2Cr2O3 0.00500.0070.005Li2O 0.59   0.63 CeO2 1.23   1.25 
TABLE I-DAdvancedIVG IVG IVG VertexGlassVertexVertexOutside #1YarnsCulimetaB96Glass GlassConstituentS GlassRoving675 YamRovingRovingSiO264.61  59.37  58.34  58.58  58.12  CaO 0.17   0.27   0.31   0.30   0.31  Al2O324.84  25.49  23.81  24.26  24.09  B2O3 0.04   0.05  MgO10.11  13.47  14.99  15.02  15.36  Na2O 0.118  0.024  0.05   0.02   0.03  Fluorine 0.03   0.04   0.04   0.04  TiO2 0.011  0.530  1.380  0.67   0.91  Fe2O3 0.042  0.374  0.333  0.336  0.303 K2O 0.48   0.42   0.28   0.29  ZrO2 0.152  0.129  0.165  0.157 Cr2O3 0.0050 0.0120 0.0100 0.0120 0.0120Li2OCeO2
TABLE I-EIVG VertexRH CG250Outside #2P109 GlassConstituentGlass RovingFiber StrandSiO258.6958.54CaO0.299.35Al2O324.325.39B2O3MgO15.066.15Na2O0.030.10Fluorine0.040.16TiO20.640.008Fe2O30.3310.069K2O0.360.14ZrO20.1870.006Cr2O30.0130Li2OCeO2
R-Glass and S-Glass are produced by melting the constituents of the compositions in a platinum-lined melting container. The costs of forming R-Glass and S-Glass fibers are dramatically higher than E-Glass fibers due to the cost of producing the fibers in such melters. Thus, there is a need in the art for methods of forming glass compositions useful in the formation of high performance glass fibers from a direct-melt process in a refractory-lined furnace and fibers formed by the method.